1. Field of the Invention
The present invention relates to a metallic sliding material usable for transportation machines, for example, motorcars and motor ships, and common industrial machines, and methods for producing the same. More particularly, the present invention relates to a metallic sliding material useful for producing parts of engines and methods of producing the same.
2. Description of the Related Art
Generally, metallic sliding members for engines are produced by working a sliding non-ferrous metal material, for example, aluminum alloy material, or a composite material made by joining a sliding non-ferrous metal alloy layer to a metallic support member into a desired form, for example, in the case of a slide bearing, the composite material is worked into a form of a cylindrical bush or a half cut cylinder.
Conventionally, copper-tin alloys and aluminum alloys have been used as an alloy for the metallic sliding materials. However, currently, to respond to requirements of high rotation speed and output of engines and of reduction in production cost of the engines, aluminum alloys and fiber-reinforced aluminum alloys are increasingly employed for the metallic sliding materials.
As an aluminum alloy for the metallic sliding materials, generally, an aluminum-tin alloy is employed. When the content of tin in the alloy is high, the resultant aluminum-tin alloy can be used even when no overlay is formed thereon. However, for a high quality metallic sliding material, the aluminum-tin alloy has relatively low content of tin of 5 to 7%, to enhance the fatigue resistance and the corrosion resistance of the alloy. In the case of the low tin content aluminum alloy, a soft tin or lead overlay coating must be formed on the aluminum alloy layer to enhance an initial running-in property of the aluminum alloy layer.
The aluminum alloys which must be plated with a overlay, are JIS 5402, AJ-1 (10%Sn-0.75%Cu-0.5%Ni and Bal. of Al), JIS 5402, AJ-2 (6%Sn-2.5%Cu-1.0% Ni and Bal. of AQ), and JIS AC8A (12%Si-1.0%Cu-1.5% Ni and Bal. of AQ).
When a soft metal overlay is formed on the aluminum alloy surface of the metallic sliding material, the resultant metallic sliding material may be disadvantageous in that when a high load is applied to the sliding material and the temperature of the sliding surface thereof is elevated due to a rise in the temperature of lubricant oil applied to the sliding surface, a fatigue phenomenon, a seizure phenomenon and/or a wearing phenomenon occurs at the sliding surface because the soft metal overlay has a low melting temperature, and thus the sliding material may become unusable.
Also, a method in which a metal material for the sliding material is mechanically worked and then an electric plating procedure is applied to the worked metal material to form an overlay thereon is known. However, this method is disadvantageous in that a plurality of working steps must be applied and thus the productivity of the method is low and the cost is high.
European Patent No. 0059273 and U.S. Pat. No. 4,836,695 for H. P. Baurels et al. discloses a slide bearing which is an example of a metallic sliding material and is produced by forming a chemical conversion coating having an excellent heat resistance on an aluminum alloy surface.
In the European patent, a zinc phosphate coating is formed on an aluminum alloy layer for the slide bearing to release a locally concentrated load on the aluminum alloy layer so as to evenly distribute the load over the sliding surface of the bearing and to enhance the running-in property of the aluminum alloy layer. The technique of the Japanese publication improves the technique of the European patent by preventing a formation of the zinc phosphate coating on the outer peripheral surface of the slide bearing layer.
Nevertheless, in the aluminum alloy slide bearings coated by the zinc phosphate coating as mentioned above, since the zinc phosphate exhibits a high crystallization property, the resultant coated sliding surface exhibits an insufficient smoothness and a low abrasion resistance and therefore, the resultant bearing material exhibits an unsatisfactory seizure resistance and abrasion resistance.
U.S. Pat. No. 4,836,695 teaches that when a slide bearing is fixed to a housing of the slide bearing, the coarse crystals of zinc phosphate coated on the back surface of the slide bearing cause the fixing of the slide bearing to the housing to be loosened. To prevent this loosening, a special treatment for preventing the formation of the zinc phosphate coating on the back surface of the slide bearing must be preliminarily applied to the back surface. This necessity is a disadvantage of the zinc phosphate coating method in practice.
Namely, it should be understood that a satisfactory surface coating for the sliding surface formed by the aluminum alloy or the fiber-reinforced aluminum alloy and having an excellent seizure resistance and a superior abrasion resistance and a method of forming the satisfactory surface coating have not yet been provided.